The invention relates to a seal stack.
Referring to FIG. 1, a downhole tool 14 may be used to perform such functions as measuring performance of a subterranean well 10 and controlling production from the well 10. As examples, the tool 14 may be part of a test string 12, part of a drill string, connected to a wireline, or connected to a slickline.
In the course of its operation, the tool 14 may be subject to a large range of temperatures and a large range of pressures. For example, the temperatures that the tool 14 may experience may vary from approximately 60xc2x0 Fahrenheit (F.) to approximately 500xc2x0 F., and the pressures may vary from approximately a few pounds per square inch (psi) to approximately 30,000 psi. These variations, in turn, may affect the performance of seals of the tool 14. As an example, referring to FIG. 2, the tool 14 may include a mandrel 22 that may move in response to pressure differences to actuate a downhole valve (not shown), for example. More particularly, the mandrel 22 may have a piston head surface 24 that is contact with fluid in one chamber 26 and another piston head surface 20 that is contact with fluid in another chamber 27. In this manner, the pressure differential between the two chambers 26 and 27 influences movement of the mandrel 22.
To isolate the two chambers 26 and 27 from each other, the tool 14 may include an annular seal 30 (a seal stack, for example) that is located in an annular cavity of the mandrel 22 and between the two piston head surfaces 20 and 24. The type of seal 30 that is used may be selected based on the expected downhole temperatures and pressures. However, the tool 14 may be used in applications that cause the tool 14 to experience a wide range of temperatures and pressures. For example, oil and gas exploration is currently advancing into the traditionally deeper and harder to reach areas in which pressures may be near 20,000 psi, and the temperature may be over 400xc2x0 F. Furthermore, operation of the tool 14 may increase the pressure to near 30,000 psi. Therefore, the seal 30 may be required to operate over a wide range of conditions.
Thus, there is a continuing need for a seal that addresses one or more of the problems stated above.
In an embodiment of the invention, a seal stack includes one or more first seals that are adapted to seal in at least a first range of temperatures. The seal stack also includes a second seal that is adjacent to at least one of the first seals. The second seal is adapted to seal in at least a lower range of temperatures than the first range of temperatures.
Advantages and other features of the invention will become apparent from the following description, drawing and claims.